To get to ffdshow's audio decoder options dialog, click on “Start” → “All programs” → “ffdshow” → “Audio decoder configuration”.
Alternatively, while playing a audio/video file, double-click the red ffdshow video icon in the notification area of the task bar. Most settings can be changed during playback and take effect immediately, while codecs, output colorspaces, queue and some other settings need a restart of the audio/video application in order to take effect.